Organic electroluminescent device and method of manufacture thereof

ABSTRACT

An organic EL device having a low driving voltage and exhibiting high luminous brightness and superior durability, and a method of manufacturing the same. The organic EL device has an anode layer, an organic light-emitting layer, and a cathode layer. An inorganic thin layer, comprising an inorganic compound of Ge, Sn, Zn, Cd, etc. and an inorganic compound of an element of Group 5A to Group 8 in the periodic table in combination, is provided between the anode layer and the organic light-emitting layer and between the cathode layer and the organic light-emitting layer, or the anode layer or the cathode layer comprises a chalcogenide of Si, Ge, Sn, Pb, Ga, In, Zn, Cd, Mg, etc. and an inorganic compound of an element of Group 5A to Group 8 in the periodic table in combination.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of application Ser. No. 09/671,296,filed on Sep. 27, 2000 now U.S. Pat. No. 6,416,888, which is aContinuation of PCT/JP00/00832, filed Feb. 15, 2000.

TECHNICAL FIELD

The present invention relates to an organic electroluminescent device(hereinafter may be called “organic EL device”) and a method ofmanufacturing the organic EL device. More particularly, the presentinvention relates to an organic EL device suitably used for displayapparatuses for home use or industrial use, light sources for printerheads, and the like, and to a method of manufacturing the organic ELdevices.

BACKGROUND ART

Development of organic EL devices with an organic light-emitting layerinserted between electrodes of the devices have intensively beenundertaken for the following reasons.

(1) Handling and production of organic EL devices become easy becausethe organic EL devices are complete solid elements.

(2) Organic EL devices do not require the additional luminousapparatuses because these devices can emit the light themselves.

(3) Organic EL devices are suitable for use with display apparatuses dueto excellent visibility.

(4) A full color display can be easily provided using the organic ELdevices.

However, because the organic light-emitting layer is an organicsubstance, injecting electrons from a cathode layer is not easy. Inaddition, because the organic substance generally can transfer electronsand positive holes only with difficulty, the organic light-emittinglayer tends to deteriorate easily and produce leakage current when usedfor a long period of time.

Japanese Patent Application Laid-open No. 8-288069 discloses an organicEL device provided with an insulating thin layer between an electrodeand an organic light-emitting layer as a means for extending the life ofthe organic EL device. The organic EL device disclosed in this patentapplication has a configuration in which an insulating thin layer ofaluminum nitride, tantalum nitride, or the like is provided between ananode layer and an organic light-emitting layer or between a cathodelayer and an organic light-emitting layer.

U.S. Pat. No. 5,853,905 discloses an organic EL device provided with aninsulating thin layer between an anode layer and a light-emitting layeror a cathode layer and a light-emitting layer. The U.S. patent alsodiscloses SiO₂, MgO, and Al₂O₃ as materials for forming the insulatingthin layers.

With an objective of providing an organic EL device at low cost withoutusing expensive materials such as4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(hereinafter may be abbreviated as “MTDATA”) and tetraaryldiaminederivatives, Japanese Patent Application Laid-open No. 9-260063discloses an organic EL device having an inorganic material layercomprising NiO and at least one compound selected from the groupconsisting of In₂O₃, ZnO, SnO₂, and compounds containing B, P, C, N, orO, or an inorganic material layer of Ni_(1−x)O (0.05≦x≦0.5) between anelectrode and an organic light-emitting layer.

With an objective of extending the life of organic EL devices byreducing the energy difference between the work function of an anodelayer and the ionization energy of a positive hole transport layer,Japanese Patent No. 2824411 discloses an organic EL device having ananode layer made of a conductive metal oxide material exhibiting a workfunction greater than indium tin oxide (ITO) such as RuO_(x), MoO₃, andV₂O₅, for example. This Japanese Patent proposes in the specification ananode layer having a two layer structure consisting of these conductivemetal oxide materials and an ITO to improve the light transmittance.

However, the inorganic compounds such as aluminum nitride, tantalumnitride, SiO₂, and the like used as an insulating thin layer in theorganic EL devices disclosed in Japanese Patent Application Laid-openNo. 8-288069 and U.S. Pat. No. 5,853,905 have a great ionizationpotential which results in an increased driving voltage. Specifically,because the inorganic thin layers consisting of these inorganiccompounds are electric insulating layers having an excessively largeionization energy, positive holes are injected from the anode layer by atunnel effect. Therefore, a high driving voltage is required between theelectrodes of the organic EL device to obtain a desired luminousbrightness.

The organic EL device disclosed in Japanese Patent Application Laid-openNo. 9-260063 is characterized by the use of NiO as a major component,which unduly limits the types of materials usable as an inorganicmaterial layer and exhibits only a low luminous efficiency.

The organic EL device disclosed in Japanese Patent No. 282411 has theproblems of small positive hole mobility and insufficient durability inspite of the use of the metal oxide materials such as RuO_(x) (1≦x≦2),MoO₃, and V₂O₅.

In addition, the metal oxide materials such as RuO_(x) (1≦x≦2), MoO₃,and V₂O₅ exhibit a large optical absorption coefficient of 27,000 cm⁻¹or more, giving rise to remarkable coloration. Therefore, the lighttransmittance in the visible radiation range of the anode layer made ofthese metal oxide materials is very low, for example, about {fraction(1/9)} to ⅕ that of ITO, giving rise to problems such as a poor luminousefficiency and a small quantity of light which can be emitted.

In addition, even an anode layer with a two-layer structure consistingof lamination of a thin film of these metal oxide materials and ITOexhibits only a small light transmittance (about ½ that of ITO). Such ananode layer cannot be used in practice. Moreover, when an anode layerhaving such a two-layer structure is fabricated, the thickness of theITO and a metal oxide film must be restricted within a prescribed range,resulting in a limitation in the manufacturing process.

The present inventors have conducted extensive studies to overcome theabove problems and have found that, even in the case where an inorganicthin layer is provided in an organic EL device, an intermediate levelfor injection of electric charges can be formed in the inorganic thinlayer by forming the inorganic thin layer from a combination of severalspecific inorganic compounds.

The inventors have further found that the combined use of specificinorganic compounds for forming the inorganic thin layer may produce anorganic EL device with excellent transparency and durability, andsuperior luminous brightness at a low applied voltage (for example, lessthan DC 10V).

Accordingly, an object of the present invention is to provide an organicEL device having a specific inorganic thin layer and exhibitingexcellent durability, a low driving voltage, and superior luminousbrightness, as well as a method of efficiently manufacturing such anorganic EL device.

Another object is to provide an organic EL device having an electrodelayer made from a combination of specific inorganic compounds andexhibiting excellent durability, a low driving voltage, and superiorluminous brightness, as well as a method of efficiently manufacturingsuch an organic EL device.

DISCLOSURE OF THE INVENTION

(1) One embodiment of the present invention (first invention) which isan organic EL device having an anode layer, an organic light-emittinglayer, and a cathode layer is characterized by having a first inorganicthin layer formed between the anode layer and the organic light-emittinglayer or a second inorganic thin layer formed between the cathode layerand the organic light-emitting layer, or having both the first and thesecond inorganic thin layers, wherein when the first inorganic thinlayer is formed between the anode layer and the organic light-emittinglayer, the intermediate level of the first inorganic thin layer is setat a value smaller than the ionization potential of the organiclight-emitting layer; when the second inorganic thin layer is formedbetween the cathode layer and the organic light-emitting layer, theintermediate level of the second inorganic thin layer is set at a valuegreater than the electron affinity of the organic light-emitting layer;and an electric charge is injected through either the intermediate levelof the first inorganic thin layer or the intermediate level of thesecond inorganic thin layer, or both.

This constitution enables charges to be injected with ease withoututilizing a tunnel effect. Thus, an excellent organic EL device having alow driving voltage and exhibiting high luminous brightness anddurability may be obtained.

The intermediate energy level in an inorganic thin layer will now beexplained referring to FIGS. 7(a) and 7(b). FIG. 7(a) shows therelationship between an intermediate level in the inorganic thin layeron the anode layer side and an energy level in the organiclight-emitting layer, and FIG. 7(b) shows the relationship between anintermediate level in the inorganic thin layer on the cathode layer sideand an energy level in the organic light-emitting layer. In FIGS. 7(a)and 7(b), the intermediate level (Ei) of the first and the secondinorganic thin layers is indicated between a valence band level (theionization potential of the inorganic thin layer, Ev) and a conductionband level (the electron affinity of the inorganic thin layer, Ec).

Specifically, the intermediate level (Ei) in this inorganic thin layeris defined as the energy level which exists between Ev and Ec.

When a first inorganic thin layer is formed between the anode layer andthe organic light-emitting layer in the present invention, theintermediate level (Ei) of the first inorganic thin layer is set at avalue smaller than the energy level directed to the ionization potential(Ip) of the organic light-emitting layer, so that positive holes may beeasily injected into the intermediate level (Ei) of the first inorganicthin layer from the anode layer as energy by applying a prescribedvoltage. The positive holes then energetically move through theintermediate level (Ei) and are easily injected into the positive holelevel (HOMO: Highest Occupied Molecular Orbital) in the organiclight-emitting layer. This movement of the positive holes isschematically indicated by a dotted line in FIG. 7(a).

On the other hand, when a second inorganic thin layer is formed betweenthe cathode layer and the organic light-emitting layer in the presentinvention, the intermediate level (Ei) of the first inorganic thin layeris set at a value larger than the energy level directed to the electronaffinity (Af) of the organic light-emitting layer, so that electrons maybe easily injected into the intermediate level (Ei) of the secondinorganic thin layer from the cathode layer as energy by applying aprescribed voltage. Then, the electrons energetically move through theintermediate level (Ei) and are easily injected into the electron level(LUMO: Lowest Unoccupied Molecular Orbital) in the organiclight-emitting layer. This movement of the electrons is schematicallyindicated by a dotted line in FIG. 7(b).

In either case, even if an inorganic thin layer is provided in theorganic EL device, positive holes and. electrons easily move in theinorganic thin layer without using a tunnel effect, whereby the drivingvoltage is decreased and luminous brightness is increased.

In addition, durability may be remarkably improved by providing aninorganic thin layer like this.

Moreover, the first inorganic thin layer formed between the anode layerand the organic luminous body have the function such as an electricbarrier which confines electrons in the LUMO level within the organiclight-emitting layer due to the wide gap of the energy level.

In the same manner, the second inorganic thin layer formed between thecathode layer and the organic luminous body have the function such as apositive hole barrier which confines positive holes in the HOMO levelwithin the organic light-emitting layer due to the wide gap of theenergy level.

An organic layer other than the organic light-emitting layer may beformed between the first inorganic thin layer and the organiclight-emitting layer in the present invention in addition to the organiclight-emitting layer. In this instance, the intermediate level of theinorganic thin layer is set smaller than the ionization potential ofthis organic layer. Therefore, in such a case the intermediate level ofthe inorganic thin layer is not always necessarily smaller than theionization potential of the organic light-emitting layer.

In the same manner, an organic layer other than the organiclight-emitting layer may be formed between the second inorganic thinlayer and the organic light-emitting layer. In this instance, theintermediate level of the inorganic thin layer is set greater than theelectron affinity of this organic layer. Therefore, in such a case theintermediate level of the inorganic thin layer is not always necessarilygreater than the electron affinity of the organic light-emitting layer.

The above-described intermediate level may be determined by measuringthe fluorescence spectrum or electronic properties, and may be easilycontrolled by changing the materials used, for example.

(2) In the first invention, it is desirable that either or both of thefirst inorganic thin layer and the second inorganic thin layer containat least one compound selected from the following group A and at leastone inorganic compound selected from the following group B.

Group A: A chalcogenide of Si, Ge, Sn, Pb, Ga, In, Zn, Cd, Mg, Al, Ba,K, Li, Na, Ca, Sr, Cs, or Rb, and a nitride thereof

Group B: A compound of an element of Group 5A to Group 8 of the periodictable

The combined use of the group A and the group B ensures formation of anintermediate level in the inorganic thin layer. Because electric chargesmay be injected at low voltage through this intermediate level, theorganic EL device not only possesses superior durability, but alsoexhibits high luminous brightness. In addition, the combined use of thegroup A and the group B does not impair transparency.

(3) In the first invention, it is desirable that the band gap energy ofthe inorganic thin layer (Ba) and the band gap energy of the organiclight-emitting layer (Bh) satisfy the relationship “Ba>Bh”.

Such a relationship improves transmittance of light and increases thequantity of light which is emitted out (an efficiency of lighttaken-out). In addition, such a relationship may increase the barriercharacteristics against electrons or positive holes, resulting in anincrease in luminous efficiency.

(4) Furthermore, in the first invention, preferably the group A is achalcogenide of Si, Ge, Sn, Zn, Al, Ba, K, Li, Na, Ca, Sr, Cs, Rb, orCd, or a nitride thereof.

Because these compounds may particularly maintain an excited state for along period of time among the group A inorganic compounds, the organicEL device may exhibit a low light-quenching property and increase thequantity of light which is emitted.

(5) Furthermore, in the first invention, preferably the group B is anoxide of Ru, V, Mo, Re, Pd, or Ir.

The use of these compounds ensures formation of an intermediate level inthe inorganic thin layer.

In addition, it is desirable that the inorganic thin layer containingthese group B is provided between the anode layer and the organiclight-emitting layer.

(6) Furthermore, in the first invention, preferably the content of thegroup B is in the range of 0.1 to 50 atomic % (hereinafter abbreviatedas atm % or at. %) for 100 atomic % of the total of the inorganic thinlayer.

This range of atomic % of the group B makes it easy to adjust theionization potential of the inorganic thin layer, while maintaining ahigh transparency (light transmittance).

(7) Furthermore, in the first invention, preferably the thickness of theinorganic thin layer is in the range of 1 to 100 nm.

This range of thickness produces an organic EL device exhibitingsuperior durability, a low driving voltage, and high luminousbrightness. In addition, the organic EL device does not become undulythick if the thickness of the inorganic thin layer is maintained in thisrange.

(8) In another embodiment of the organic EL device of the presentinvention (second invention) which comprises an anode layer, an organiclight-emitting layer, and a cathode layer, either the anode layer or thecathode layer or both comprise at least one compound selected from thefollowing group A-1 and at least one compound selected from thefollowing group B-1, or at least one compound selected from thefollowing group A-2 and at least one compound selected from thefollowing group B-2.

Group A-1: A chalcogenide of Si, Ge, Sn, Pb, Ga, In, Zn, Cd, Mg, Al, Ba,K, Li, Na, Ca, Sr, Cs, or Rb, and a nitride thereof

Group B-1: Inorganic compounds of an element of Group 5A to Group 8 inthe periodic table and carbon.

Group A-2: A chalcogenide of Ge, Sn, Pb, Ga, In, Zn, Cd, Mg, Al, Ba, K,Li, Na, Ca, Sr, Cs, or Rb, and a nitride thereof

Group B-2: Inorganic compounds of an element of Group 5A to Group 8 inthe periodic table, chalcogenide of Si and a nitride thereof, andcarbon.

The combined use of the group A-1 and group B-1, or of the group A-2 andgroup B-2 may efficiently increase the ionization potential of theelectrode layer. Specifically, the electrode layer has an ionizationpotential of 5.4 eV or more. Therefore, an organic EL device exhibitingdurability, a low driving voltage, and high luminous brightness may beobtained.

In addition, the thus obtained electrode layer may exhibit excellentetching characteristics.

Furthermore, if the electrode layer contains a chalcogenide of Si or anitride in at least one of the group A-1 and group B-1, or at least oneof the group A-2 and group B-2, adherence between the substrate and theelectrode layer is further improved and the electrode layer may beformed more uniformly.

When forming an anode layer using these inorganic compounds, it isdesirable to set the work function at 4.0 eV or more taking into accountinjection characteristics of positive holes. On the other hand, whenforming a cathode layer using these inorganic compounds, the workfunction is preferably set at less than 4.0 eV taking into accountinjection characteristics of electrons.

(9) Furthermore, in the second invention, preferably either the anodelayer or the cathode layer or both has a specific resistance of lessthan 1 Ω·cm.

This is because high resistance of the electrode layer preventsuniformity of luminescence. Therefore, not only may injectioncharacteristics of electrons and positive holes be improved, but alsothe driving voltage of the organic EL device may be more decreased byrestricting the specific resistance in this manner.

On the other hand, if a material for forming electrode layers has aspecific resistance of more than 1 Ω·cm, such a material may be usedpreferably for forming a two-layer structure in combination with anothermaterial having a specific resistance of less than 1 Ω·cm.

(10) Furthermore, in the second invention, the inorganic compound ofgroup A-1 or group A-2 is preferably a chalcogenide of Sn, In, or Zn ora nitride thereof.

This is because, among inorganic compounds of group A-1 and group A-2,these inorganic compounds may have particularly small light-quenchingcharacteristics.

Among these inorganic compounds, chalcogenides consisting ofcombinations of In and Zn are particularly preferred. Because the thinlayer consisting of a combination of these inorganic compounds may havea flat surface, the film may have the stable amorphous properties. Athin layer made of a chalcogenide containing only In or In and Sn mayhave a surface less flat than that of the thin layer made from achalcogenide containing In and Zn, because the former is crystalline orunstable amorphous.

(11) Furthermore, in the second invention, the compound of group B-1 orgroup B-2 is preferably an oxide (inorganic compound) of Ru, Re, V, Mo,Pd, or Ir.

The combined use of these inorganic compounds may make it easy to adjustthe ionization potential and band gap energy in the electrode layers.

(12) Furthermore, in the second invention, preferably the content of thegroup B-1 or group B-2 is in the range of 0.5 to 30 atomic % for 100atomic % of the total of the anode layer or the cathode layer.

This range of atomic % of the group B-1 or group B-2 may make it easy toadjust the ionization potential of the electrode layer, whilemaintaining a high transparency (light transmittance). In addition, theelectrode layer thus obtained may exhibit excellent etchingcharacteristics when an acid or the like is used as an etching agent.

(13) Furthermore, in the second invention, the anode layer or thecathode layer preferably has a thickness in the range of 1 to 100 nm.

This range of thickness may produce an organic EL device exhibitingsuperior durability, a low driving voltage, and high luminousbrightness. In addition, the organic EL device does not become undulythick if the thickness of the electrode layer is maintained in thisrange.

(14) Furthermore, in the first and the second inventions, the organiclight-emitting layer preferably contains at least one of the aromaticcompounds having a styryl group represented by the following formulas(1) to (3).

wherein Ar¹ is an aromatic group having 6 to 50 carbon atoms, Ar², Ar³,and Ar⁴ are individually a hydrogen atom or an aromatic group having 6to 50 carbon atoms, provided that at least one of Ar¹, Ar², Ar³, and Ar⁴is an aromatic group, and n, which indicates a condensation number, isan integer from 1 to 6.

wherein Ar⁵ is an aromatic group having 6 to 50 carbon atoms, Ar⁶ andAr⁷ are individually a hydrogen atom or an aromatic group having 6 to 50carbon atoms, provided that at least one of Ar⁵, Ar⁶, and Ar⁷ has astyryl group which may have a substituent, and m, which indicates acondensation number, is an integer from 1 to 6.

wherein Ar⁸ and Ar¹⁴ are individually an aromatic group having 6 to 50carbon atoms, Ar⁹ to Ar¹³ are individually a hydrogen atom or anaromatic group having 6 to 50 carbon atoms, provided that at least oneof Ar⁸ to Ar¹⁴ has a styryl group which may have a substituent, and p,q, r, and s, which indicate condensation numbers, are individually 0 or1.

(15) Another embodiment of the present invention (third invention) is amethod for manufacturing any one of the above-described organic ELdevices, which preferably comprises forming at least one layer in anorganic electroluminescence by either a sputtering method or a vacuumdeposition method, or both, by using a rotation evaporation apparatuscapable of simultaneous evaporation.

This method ensures production of a thin layer with a uniform ratio ofcomponents even if a plurality of compounds is used, which consequentlyenables efficient manufacture of organic EL devices exhibiting highluminous brightness at a low driving voltage, and having excellentdurability.

(16) In the third invention, preferably the inorganic thin layer isformed by a sputtering method and the organic light-emitting layer isformed by a vacuum deposition method.

This method of forming ensures production of an inorganic thin layer andan organic light-emitting layer having a precise and uniform thickness.Therefore, an organic EL device which has a uniform luminous brightnessmay be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of the organic EL device in thefirst and the second embodiments.

FIG. 2 shows a cross-sectional view of the organic EL device in thethird embodiment.

FIG. 3 shows a cross-sectional view of the organic EL device in thefourth embodiment.

FIG. 4 shows a perspective view of the vacuum deposition apparatus inthe fifth embodiment.

FIG. 5 shows a cross-sectional view of the vacuum deposition apparatusin the fifth embodiment.

FIG. 6 is a drawing describing measuring points in a substrate.

FIG. 7 is a drawing describing an intermediate level.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention (first to third inventions) will beexplained with references to the drawings. The drawings schematicallyshow the sizes, shapes, and positional relationships of the componentsto assist understanding of the present invention. Accordingly, thepresent invention shall not be limited to the embodiments shown in thedrawings. Hatching to indicate sections is sometimes omitted in thedrawing.

(First Embodiment)

A first embodiment according to the first invention will be explainedwith reference to FIG. 1. FIG. 1 shows a sectional view of an organic ELdevice 102 formed by successively laminating an anode layer 10, aninorganic thin layer 12, an organic light-emitting layer 14, and acathode layer 16 on a substrate (not shown in the drawing).

The first embodiment will now be explained focusing on the inorganicthin layer 12 and the organic light-emitting layer 14 which arecharacteristic in the first embodiment. Therefore, configurations andmethods of manufacture of other components such as, for example, theanode layer 10 and cathode layer 16 are only briefly explained, andconventionally known configurations and methods of manufacture in thefield of organic EL devices can be applied to the other parts which arenot mentioned here.

(1) Inorganic Thin Layer

Materials

The first and second inorganic thin layers (hereinafter may be simplyreferred to as “inorganic thin layer”) must comprise the inorganiccompounds of the following group A and group B in combination.

Group A: A chalcogenide of Si, Ge, Sn, Pb, Ga, In, Zn, Cd, Mg, Al, Ba,K, Li, Na, Ca, Sr, Cs, or Rb, or a nitride thereof

Group B: Compounds of an element of Group 5A to Group 8 of the periodictable

The reason is that only the combination of the inorganic compounds ofgroup A and group B may produce an organic EL device exhibiting superiordurability, a low driving voltage, and high luminous brightness. Ifeither the group A or the group B is solely used, it is difficult toform an intermediate level in the inorganic thin layer. Therefore, it isimpossible to decrease the driving voltage or improve durability.

Given as preferable inorganic compounds of group A are SiO_(x) (1≦x≦2),GeO_(x) (1≦x≦2), SnO₂, PbO, In₂O₃, ZnO, GaO, CdO, MgO, SiN, GaN, ZnS,ZnSe, CdS, CdSe, ZnSSe, CaSSe, MgSSe, GaInN, LiO_(x) (1≦x≦2), SrO,CsO_(x) (1≦x≦2), CaO, NaO_(x) (1≦x≦2), mixtures of these inorganiccompounds, and laminates of these inorganic compounds.

Among these group A, a chalcogenide of Si, Ge, Sn, Zn, Cd, Mg, Ba, K,Li, Na, Ca, Sr, Cs, or Rb, and a nitride thereof are preferable.

The reason is that, as partly mentioned above, because these inorganiccompounds have a small absorption coefficient, particularly smalllight-quenching characteristics, and superior transparency among thegroup A inorganic compounds, it is possible to increase the amount oflight which is emitted out.

Preferable inorganic compounds of group A are chalcogenide compounds ofSi, Ge, Sn, Zn, Cd, Mg, Al, Ba, K, Li, Na, Ca, Sr, Cs, or Rb, andparticularly oxides thereof.

Specific examples of the group B are RuO_(x) (1≦x≦2), V₂O₅, MoO₃, Ir₂O₃,NiO₂, RhO₄, ReO_(x) (1≦x≦2), CrO₃, Cr₂O₃, RhO_(x) (1≦x≦2), MoO_(x)(1≦x≦2), and VO_(x) (1≦x≦2). These compounds may be used eitherindividually or in combinations of two or more.

Among these group B, oxides of Ru, Re, V, Mo, Pd, and Ir, specifically,RuO_(x) (1≦x≦2), ReO_(x) (1≦x≦2), V₂O₅, MoO₃, MoO_(x) (1≦x≦2), PdO₂, andIr₂O₃ are preferable. The use of these group B ensures formation of anintermediate level in the inorganic thin layer, allowing easy injectionof electric charges.

Content

Next, the content of the group B is described. The content of the groupB is preferably in the range of 0.1 to 50 atomic % for 100 atomic % ofthe total of the inorganic thin layer.

If the content of the group B is less than 0.1 atomic %, an intermediatelevel may not be formed in the inorganic thin layer; if more than 50atomic %, the inorganic thin layer may be colored or the transparency(light transmittance) may be impaired.

Therefore, in view of balancing formation of an intermediate level inthe inorganic thin layer, and transparency, the content of the group Bis more preferably in the range of 1 to 30 atomic %, and most preferably2 to 20 atomic %, for 100 atomic % of the total of the inorganic thinlayer.

When an inorganic thin layer is composed of the inorganic compounds ofgroup A and group B, the content of the group A is equivalent to thetotal amount (100 atomic %) minus the content of the group B. Therefore,when the content of the group B is in the range of 0.1 to 50 atomic %,the content of the group A is in the range of 50 to 99.9 atomic %.However, when a compound other than the group A or the group B (a thirdcomponent) is present, it is desirable to decide the content of thegroup A taking into account the content of the third component in theinorganic thin layer.

Thickness

Although the thickness of the inorganic thin layer is not specificallyrestricted, such a thickness is preferably in the range of 0.5 to 100nm. If the thickness of the inorganic thin layer is less than 0.5 nm,pin-holes may be produced and a leakage current may be observed when thelayer is used for a long time; if more than 100 nm, on the other hand,the driving voltage may increase and luminous brightness may decline.

Therefore, in view of maintaining well balanced durability and a drivingvoltage, the thickness of the inorganic thin layer is in the range of0.5 to 50 nm, and preferably 0.5 to 5 nm.

Method of Formation

Next, methods of forming the inorganic thin layer will be explained.Although the method is not specifically limited, a sputtering method,vapor deposition method, spin coat method, casting method, LB method(Langmuir-Blodgett method), and the like may be employed. A radiofrequency magnetron sputtering method is particularly preferred.

When using the radio frequency magnetron sputtering method, it isdesirable to perform sputtering in an inert gas under vacuum of 1×10⁻⁷to 1×10⁻³ Pa, a layer forming speed of 0.01 to 50 nm/second, and asubstrate temperature of −50° C. to 300° C.

Light-Emitting Mechanism

Next, the light emitting mechanism when the inorganic thin layercomprising the inorganic compounds of group A and group B is providedwill be explained.

As previously mentioned, a conventional organic EL device having aninorganic thin layer consisting of AlN, TaN, and the like has a problemof requiring a high driving voltage because of utilization of a tunneleffect.

Therefore, as previously mentioned, an intermediate level is provided inthe inorganic thin layer in the present invention to enable the organicEL device to be driven at a low voltage and to exhibit high luminousbrightness. More specifically, by forming an inorganic thin layer fromthe inorganic compounds of group A and group B, the energy level of theinorganic thin layer is maintained between the energy level of theelectrode layer (anode layer, or cathode layer) and the energy level ofthe organic light-emitting layer. Electric charges are injected throughthe intermediate level (Ei) thus formed. Because electric charges areeasily injected into an organic light-emitting layer in this manner, notonly may the organic EL device be driven at a low voltage, but it alsoexhibits high luminous brightness. In addition, durability of theorganic EL device is remarkably improved due to the low driving voltage.

The intermediate level (Ei) in the inorganic thin layer may exist eitherinside the inorganic thin layer or in the interface of the inorganicthin layer and the organic light-emitting layer.

In addition, it is desirable to set the energy level (Ec) of theinorganic thin layer at a value smaller than the work function of theanode layer (Wa), to prevent electrons from passing through the organiclight-emitting layer. In other words, higher luminous brightness may beobtained if the inorganic thin layer is provided with an electronicbarrier.

For the same purpose, it is desirable to set the energy level (Ev) ofthe inorganic thin layer greater than the work function of the cathodelayer(Wc), so that positive holes may not pass through the organiclight-emitting layer. Specifically, it is possible to cause theinorganic thin layer of the present invention to exhibit the barriercharacteristics against positive holes by using a wide gap inorganicthin layer.

(2) Organic Light-Emitting Layer

Function

The organic light-emitting material used as a material for the organiclight-emitting layer preferably has the following three functions at thesame time.

(a) Electric charge injecting function: the function of allowingpositive holes to be injected from the anode layer or the positive holeinjection layer during application of electric field and, at the sametime, allowing electrons to be injected from the cathode layer or theelectron injection layer.

(b) Transport function: the function of allowing injected positive holesand electrons to move by the force of an electric field.

(c) Light-emitting function: the function of providing the field forelectrons and positive holes to re-associate, causing them to emitlight.

The material does not necessarily possess all of the functions (a) to(c). Some material which exhibits more excellent positive hole injectingand transporting characteristics than electron injecting andtransporting characteristics, for example, is suitable as an organicluminescent material. Therefore, a material which may accelerate themovement of electrons in the organic light-emitting layer and may causethe electrons to recombine with positive holes around the center of theorganic light-emitting layer is suitably used.

Mobility

To improve recombining capability in the organic light-emitting layer,the electron mobility of the organic light-emitting material ispreferably 1×10⁻⁷ cm²/V·s or more. If less than 1×10⁻⁷ cm²/V·s, ahigh-speed response in the organic EL device may become difficult andthe luminous brightness may decline.

Therefore, the electron mobility of the organic light-emitting materialis more preferably in the range of 1×10⁻⁷ to 2×10⁻³ cm²/V·s, andparticularly preferably 1.2×10⁻⁷ to 1.0×10⁻³ cm²/V·s.

The reason for restricting the electron mobility to a value smaller thanthe positive hole mobility of the organic light-emitting material in theorganic light-emitting layer is that otherwise not only the organiclight-emitting materials usable for the organic light-emitting layer maybe unduly limited, but also luminous brightness may decline. On theother hand, the electron mobility of the organic light-emitting materialis preferably greater than {fraction (1/1,000)} of the positive holemobility. The reason is that if the electron mobility is excessivelysmall, it may be difficult for the electrons to recombine with positiveholes around the center of the organic light-emitting layer and theluminous brightness may decline.

Therefore, the relationship between the positive hole mobility (μ_(h))and the electron mobility (μ_(e)) of the organic light-emitting materialin the organic light-emitting layer should preferably satisfy theinequality of μ_(h)/2>μ_(c)>μ_(h)/500, and more preferably ofμ_(h)/3>μ_(c)>μ_(h)/100.

Materials

Furthermore, in the first embodiment, it is desirable that the organiclight-emitting layer contain one or more aromatic compounds having astyryl group represented by the following formulas (1) to (3) describedabove (such an aromatic compound may be called “a styrylgroup-containing aromatic compound”). The above-mentioned conditions forthe electron mobility and the positive hole mobility of the organiclight-emitting material in the organic light-emitting layer may beeasily satisfied by using such a styryl group-containing aromaticcompound.

In the formula (1) to (3) representing preferable styrylgroup-containing aromatic ring compounds, as aryl groups having 5 to 50nucleus atom numbers among aromatic groups having 6 to 50 carbon atoms,phenyl, naphthyl, anthranyl, phenanthryl, pyrenyl, cholonyl, biphenyl,terphenyl, pyrrolyl, furanyl, thiophenyl, benzothiophenyl, oxadiazolyl,diphenylanthranyl, indolyl, carbazolyl, pyridyl, benzoquinolyl, and thelike would be given.

As preferable arylene groups having 5 to 50 nucleus atom numbers,phenylene, naphthylene, anthranylene, phenanthrylene, pyrenylene,cholonylene, biphenylene, terphenylene, pyrrolylene, furanylene,thiophenylene, benzothiophenylene, oxadiazolylene, diphenylanthranylene,indolylene, carbazolylene, pyridylene, benzoquinolylene, and the likemay be given.

The aromatic group having 6 to 50 carbon atoms may have a substituent.Given as preferable substituents are alkyl groups having 1 to 6 carbonatoms such as an ethyl group, methyl group, 1-propyl group, n-propylgroup, s-butyl group, t-butyl group, pentyl group, hexyl group,cyclopentyl group, and cyclohexyl group; alkoxy groups having 1 to 6carbon atoms such as an ethoxy group, methoxy group, 1-propoxy group,n-propoxy group, s-butoxy group, t-butoxy group, pentoxy group, hexyloxygroup, cyclopentoxy group, and cyclohexyloxy group; aryl groups having 5to 50 nucleus atom numbers, amino groups substituted by an aryl grouphaving 5 to 50 nucleus atom numbers, ester groups substituted by an arylgroup having 5 to 50 nucleus atom numbers, ester groups substituted byan alkyl group having 1 to 6 carbon atoms, a cyano group, a nitro group,and halogen atoms. The above-mentioned substituents may be furthersubstituted by a styryl group.

As specific examples of preferable aromatic compounds having a styrylgroup shown by the formula (1), compounds shown by the followingformulas (4) to (13) may be given.

As specific examples of preferable aromatic compounds having a styrylgroup shown by the formula (2), compounds shown by the followingformulas (14) to (35) may be given.

As specific examples of preferable aromatic compounds having a styrylgroup shown by the formula (3), compounds shown by the followingformulas (36) to (44) may be given.

The organic light-emitting layer may further comprise other compounds.Such other compounds include fluorescent whitening agents such asbenzothiazoles, benzoimidazoles, benzooxazoles, and the like;styrylbenzene compounds; and metal complexes having an 8-quinolinolderivative as a ligand which are typified by Alq of the followingformula (45).

Furthermore, an organic light-emitting material having a distyrylaryleneskeleton, for example, a material prepared by reacting a host substancesuch as 4,4′-bis(2,2-diphenylvinyl)biphenyl, and a strong fluorescentdye with a color from blue to red, such as a cumarin-based fluorescentdye, or a material doping other fluorescent dye having a similar colorto the host substance, may be suitably used together.

Method of Formation

Next, methods of forming the organic light-emitting layer will beexplained. Although the method of forming is not specifically limited, avacuum deposition method, spin coating method, casting method, LBmethod, sputtering method, and the like may be employed. When using avacuum deposition method, vacuum deposition is preferably performed at avacuum deposition temperature of 50 to 450° C. in an inert gas, undervacuum of 1×10⁻⁷ to 1×10⁻³ Pa, a layer forming speed of 0.01 to 50nm/second, and a substrate temperature of −50° C. to 300° C.

The organic light-emitting layer may be also formed by dissolving abinding agent and an organic light-emitting material in a solvent toobtain a solution and by spin-coating the solution to form a thin layer.

In addition, the organic light-emitting layer is preferably a thin layerformed by deposition of a gaseous material by suitably selectinglayer-forming methods and conditions, or a molecular deposition layermade by solidification of raw material compounds which are in the formof a solution or a liquid. Such a molecular deposition layer can bedistinguished from a thin layer (molecular accumulation layer) formed bythe LB method by the differences of aggregation structure and highdimensional structure as well as by the functional differences thereof.

Thickness

The thickness of the organic light-emitting layer is not specificallylimited and may be appropriately selected according to the conditions.Preferably, the thickness is in the range of 5 nm to 5 μm. If thethickness of the organic light-emitting layer is less than 5 nm,luminous brightness and durability may be impaired; if more than 5 μm,on the other hand, the applied voltage may increase.

Therefore, in view of maintaining well balanced luminous brightness,applied voltages, and the like, the thickness of the organiclight-emitting layer is preferably in the range of 10 nm to 3 μm, andmore preferably 20 nm to 1 μm.

(3) Electrodes

Anode Layer

As an anode layer, metals, alloys, electrically conductive compoundswith a large work function (for example, 4 eV or more), or mixturesthereof may be used. Specifically, indium tin oxide (ITO), indium,copper, tin, zinc oxide, gold, platinum, palladium, carbon, and the likemay be used either individually or in combinations of two or more.

Although the thickness of the anode layer is not specificallyrestricted, such a thickness is preferably in the range of 10 to 1,000nm, and more preferably 10 to 200 nm.

Furthermore, in order to effectively remove light emitted from theorganic light-emitting layer, the anode layer should be substantiallytransparent. Specifically, the anode layer has light transmittance of10% or more, and preferably 70% or more.

Cathode Layer

As an cathode layer, metals, alloys, electric conductive compounds witha small work function (for example, less than 4 eV), or mixtures thereofmay be used. Specifically, magnesium, aluminum, indium, lithium, sodium,cesium, silver, and the like may be used either individually or incombination of two or more.

Although the thickness of the cathode layer is not specificallyrestricted, such a thickness is preferably in the range of 10 to 1,000nm, and more preferably 10 to 200 nm.

(4) Others

Although not shown in FIG. 1, it is desirable to provide a sealing layerto cover the entire organic EL device to prevent water and oxygen fromentering.

The following materials (a) to (h) may be given as examples of amaterial preferably used as a sealing layer.

(a) A copolymer obtained by the polymerization of a monomer mixturewhich contains tetrafluoroethylene and at least one comonomer.

(b) Fluorine-containing copolymers having a cyclic structure in thecopolymer main chain.

Copolymers of polyethylene, polypropylene, polymethylmethacrylate,polyimide, polyurea, polytetrafluoroethylene,polychlorotrifluoroethylene, polydichlorodifluoroethylene, orchlorotrifluoroethylene and dichlorodifluoroethylene.

(c) Hygroscopic materials having a water absorption rate of 1% or moreor moisture preventing materials.

(d) Metals such as In, Sn, Pb, Au, Cu, Ag, Al, Ti, and Ni.

(e) Metal oxides such as MgO, SiO, SiO₂, GeO, NiO, CaO, BaO, Fe₂O, Y₂O₃,and TiO₂.

(f) Metal flurorides such as MgF₂, LiF, AlF₃, and CaF₂.

(g) Liquid fluorocarbons such as perfluoroalkanes, perfluoroamines, andperfluoropolyethers.

(h) Compositions comprising a liquid fluorocarbon and an adsorbentcapable of adsorbing water and oxygen dispersed in the liquidfluorocarbon.

A vacuum deposition method, spin coat method, sputtering method, castmethod, MBE (molecular beam epitaxy) method, cluster ion beam vapordeposition method, ion plating method, plasma polymerization method(radio frequency exciting ion plating method), plasma CVD (ChemicalVapor Deposition) method, laser CVD method, heat CVD method, gas sourceCVD method, and the like may be appropriately used for forming thesealing layer.

(Second Embodiment)

A second embodiment based on the second invention will be describedbelow. The second embodiment is an organic EL device 102, which is thesame as the above-mentioned first embodiment shown in FIG. 1, except foran improvement in the anode layer 10.

The second embodiment will now be explained focusing on the anode layer10 which is characteristic in the second embodiment. Therefore,configurations and methods of manufacture of other components such as,for example, the organic light-emitting layer 14 and the like are onlybriefly explained, and conventionally known configurations and methodsof manufacture in the field of organic EL devices can be applied to theother parts which are not mentioned here.

In the second embodiment, although the anode layer 10 shown in FIG. 1 isformed from the compounds of group A (group A-1 or group A-2) and groupB (group B-1 or group B-2), these inorganic compounds may be used forthe cathode layer 16, provided that the work function is less than 4.0eV.

It is needless to mention that an inorganic thin layer 12 may be omittedinasmuch as the second embodiment is based on the second invention.

(1) Materials

The anode layer must contain a combination of an inorganic compound ofthe following group A-1 and a compound of the following group B-1, or acombination of an inorganic compound of the following group A-2 and acompound of the following group B-2. Part of the compounds in thecombinations of an inorganic compound of the group A-1 and a compound ofthe group B-1, and the combinations of an inorganic compound of thegroup A-2 and a compound of the group B-2 overlap.

Group A-1: A chalcogenide of Si, Ge, Sn, Pb, Ga, In, Zn, Cd, Mg, Al, Ba,K, Li, Na, Ca, Sr, Cs, or Rb, and a nitride thereof

Group A-2: A chalcogenide of Ge, Sn, Pb, Ga, In, Zn, Cd, Mg, Al, Ba, K,Li, Na, Li, Ca, Sr, Cs, or Rb, and a nitride thereof

Group B-1: Compounds of an element of Group 5A to Group 8 in theperiodic table and carbon.

Group B-2: Inorganic compounds of an element of Group 5A to Group 8 inthe periodic table, chalcogenide of Si and a nitride thereof, andcarbon.

As mentioned above, it may be difficult to efficiently increase theionization potential to a value above 5.4 eV if only one of thecompounds (either an organic compound or an inorganic compound) is used.

Therefore, only the combined use of the inorganic compound of group A-1and the compound of group B-1, or the combined use of the inorganiccompound of group A-2 and the compound of group B-2 as an anode layermay produce an organic EL device exhibiting excellent durability andtransparency, a low driving voltage (a low specific resistance), andhigh luminous brightness.

The compounds in the combination of the inorganic compound of group A-1and the compound of group B-1, or the combination of the inorganiccompound of group A-2 and the compound of group B-2 excel in etchingcharacteristics when etched using an acid, for example, hydrochloricacid or oxalic acid. Such compounds produce a smooth cross-section inthe interface of an acid treated area and a non-treated area, enabling aclear distinction between acid treated areas and non-treated areas.Therefore, the electrode layer made from such inorganic compounds mayproduce electrode patterns with excellent etching precision and is freefrom breakage, deformation, and an increase in resistance, even if theelectrode is very small or the configuration is complex.

Given as preferable inorganic compounds of group A-1 are SiO_(x)(1≦x≦2), GeO_(x) (1≦x≦2), SnO₂, PbO, In₂O₃, ZnO, GaO, CdO, ZnS, ZnCe,CdSe, In_(x)Zn_(y)O (0.2≦x/(x+y)≦0.95), ZnOS, CdZnO, CdZnS, MgInO,CdInO, MgZnO, GaN, InGaN, MgZnSSe, LiO_(x) (1≦x≦2), SrO, CsO_(x)(1≦x≦2), CaO, NaO_(x) (1≦x≦2), and the like. As an inorganic compound ofgroup A-2, the inorganic compound of group A-1, excluding SiO_(x)(1≦x≦2), can be given.

Here, ZnO means oxides of Zn and ZnS means sulfides of Zn, wherein theratio of Zn and O or Zn and S is not necessarily 1:1, but any otherratios are acceptable.

Among the inorganic compounds of group A-1 and group A-2, chalcogenidesof Sn, In, or Zn, and a nitride thereof are preferable. The reason isthat, as partly mentioned above, because these inorganic compounds ofgroup A-1 and group A-2 have a small absorption coefficient,particularly small light-quenching characteristics, and superiortransparency, it is possible to increase the amount of light which canbe emitted out.

Among the inorganic compounds of group A-1 and group A-2, chalcogenidesconsisting of a combination of In and Zn are particularly preferable.The reason is that the inorganic compound which contains thiscombination is non-crystalline, and not only has excellent etchingcharacteristics or pattern characteristics, but also may produce aninorganic thin layer with excellent evenness.

Among chalcogenide compounds of Ge, Sn, Zn, or Cd, oxides areparticularly preferable. Furthermore, the group A-1 compounds containingat least either In or Zn are desirable.

As preferable compounds of group B-1 inorganic compounds, RuO_(x)(1≦x≦2), ReO_(x) (1≦x≦2), V₂O₅, MoO₃, PdO₂, Ir₂O₃, RhO₄, CrO₃, Cr₂O₃,MoO_(x) (1≦x≦2), WO_(x) (1≦x≦2), CrO_(x) (1≦x≦2), Nb₂O₅, NbO_(x) (1≦x≦2), PdO_(x) (1≦x≦2), and C (carbon) can be given. These compounds maybe used either individually or in combination of two or more.

As preferable compounds of group B-2, in addition to the compounds ofgroup B-1, SiO, SiO₂, SiON, or SiN_(x) (1≦x≦3/2), and the like can begiven. These compounds may be used either individually or in combinationof two or more.

Among these group B-1 and B-2 compounds, oxides of Ru, Re, V, Mo, Pd,and Ir, specifically, RuO_(x) (1≦x≦2), ReO_(x) (1≦x≦2), V₂O₅, MoO₃,PdO₂, and Ir₂O₃ are preferable. As partly mentioned above, it ispossible to efficiently increase the ionization potential in the anodelayer by using these inorganic compounds.

In addition, compounds containing Pd are particularly preferable amongthe compounds of group B-1 and group B-2. A maximum ionization potentialmay be obtained if the anode layer contains Pd.

Furthermore, to improve adherence between the anode layer and thesubstrate when a chalcogenide of Si or a nitride thereof is not includedin the compound of group A-2, it is desirable to select a chalcogenideof Si or a nitride thereof as the compound of group B-2.

(2) Content

The content of the group B compounds (compounds of group B-1 or groupB-2 may be simply called “group B compounds) will be explained. Thecontent of the group B compound is preferable in the range of 0.5 to 30atomic % for 100 atomic % of the total of the anode layer. If thecontent of the group B compound is less than 0.5 atomic %, it may bedifficult to adjust the ionization potential of the anode layer to therange of 5.40 to 5.70 eV. On the other hand, if the content of the groupB compound is more than 30 atomic %, the anode layer may have a lowconductivity, may be colored, or may exhibit impaired transparency(light transmittance).

Therefore, in view of easy adjustment of the ionization potential andwell balanced transparency and the like in the anode layer, the contentof the group B compound is preferably in the range of 0.8 to 20 atomic%, and more preferably 1 to 10 atomic %, for 100 atomic % of the totalof the anode layer.

The content of the group A compounds (compounds of group A-1 or groupA-2 may be simply called “group A compounds) is the total of the anodelayer (100 atomic %) minus the content of the group B compounds when theanode layer is made from the group A compounds (group A-1 or group A-2)and the group B compounds (group B-1 or group B-2). Therefore, when thecontent of the group B compounds is 0.5 to 30 atomic %, the content ofthe group A compounds is in the range of 70 to 99.5 atomic %.

However, when a compound other than the compounds of group A or group B(a third component) is present, it is desirable to decide the content ofthe group A compounds taking into account the content of the thirdcomponent in the anode layer.

(3) Thickness and Configuration

Although the thickness of the anode layer is not specificallyrestricted, such a thickness is preferably in the range of 0.5 to 1,000nm.

If the thickness of the anode layer is less than 0.5 nm, pin-holes maybe produced and a leakage current may be observed when the layer is usedfor a long period of time; if more than 1,000 nm, on the other hand,transparency of the electrode may be impaired, resulting in low luminousbrightness.

Therefore, in view of maintaining well balanced durability and lowdriving voltage, the thickness of the anode layer is more preferably inthe range of 1 to 800 nm, and still more preferably 2 to 300 nm.

There is no specific limitation to the configuration of the anode layer.Either a mono-layer configuration or a multi-layer (two or more layers)configuration is acceptable. Therefore, if high transparency (high lighttransmittance) and high conductivity is desired, a double layerstructure consisting of laminated layers such as a layer of ITO,In₂O₃—ZnO, or InZnO, or a metal layer, for example, is preferable.

(4) Specific Resistance

Next, the specific resistance of the anode layer will be described.Although not specifically limited, the specific resistance is preferablyless than 1 Ω·cm, for example. If the specific resistance is 1 Ω·cm ormore, not only may the luminosity inside the pixels become uneven, butalso the driving voltage of the organic EL device may increase.Therefore, to achieve a low driving voltage, the specific resistance ofthe anode layer is preferably 40 mΩ·cm or less, and more preferably 1mΩ·cm or less.

The specific resistance of the anode layer can be determined from asurface resistance measurement using a four probe method resistancemeasurement apparatus and a thickness which is separately measured.

(5) Method of Formation

Next, methods of forming the anode layer will be explained. Although themethod is not specifically limited, a sputtering method, vapordeposition method, spin coat method, sol-gel method by means of casting,spray pyrolysis method, ion-plating method, and the like can beemployed. A radio frequency magnetron sputtering method is particularlypreferred.

More specifically, sputtering conditions of a vacuum degree of 1×10⁻⁷ to1×10⁻³ Pa, a layer forming speed of 0.01 to 50 nm/second, and asubstrate temperature of −50° C. to 300° C. are preferable.

(Third Embodiment)

A third embodiment of the present invention will be explained withreference to FIG. 2. FIG. 2 shows a sectional view of an organic ELdevice 104 of the third embodiment formed by successively laminating ananode layer 10, an inorganic thin layer 12, a positive hole transportlayer 13, an organic light-emitting layer 14, and a cathode layer 16 ona substrate (not shown in the drawing).

Injected positive holes may be effectively transported by providing thepositive hole transport layer 13. Therefore, transfer of positive holesto the organic light-emitting layer becomes easy and high-speed responseof the organic EL device is ensured by providing the positive holetransport layer 13.

The organic EL device 104 of the third embodiment shown in FIG. 2 hasthe same configuration as the organic EL device 102 of the first and thesecond embodiments, except for the insertion of the positive holetransport layer 13 between the inorganic thin layer 12 and the organiclight-emitting layer 14. Accordingly, the following description isfocused on the positive hole transport layer 13 which is characteristicof the third embodiment. Other parts such as the anode layer 16, theorganic light-emitting layer 14, and the like are the same as those inthe first and the second embodiments.

(1) Materials

The positive hole transport layer is preferably formed from an organiccompound or an inorganic compound. As examples of such an organiccompound, phthalocyanine compounds, diamine compounds,diamine-containing oligomers, thiophene-containing oligomers, and thelike can be given. As examples of desirable inorganic compounds,amorphous silicon (α-Si), α-SiC, microcrystal silicon (μC-Si), μC-SiC,group II-VI compounds, group III-V compounds, amorphous carbon,crystalline carbon, diamond, and the like can be given.

(2) Configuration and Forming Method

The positive hole transport layer is not limited to a mono-layer, butmay be a double or triple layer. Although the thickness of the positivehole transport layer is not specifically restricted, this thickness ispreferably in the range of 0.5 nm to 5 μm, for example.

There are also no specific limitations to the method of forming thepositive hole transport layer. The same method of forming as applied tothe formation of positive hole injection layers can be employed.

(Fourth Embodiment)

A fourth embodiment of the present invention will be explained withreference to FIG. 3. FIG. 3 shows a sectional view of an organic ELdevice 106 of the fourth embodiment formed by successively laminating ananode layer 10, an inorganic thin layer 12, a positive hole transportlayer 13, an organic light-emitting layer 14, and an electron injectionlayer 15 on a substrate (not shown in the drawing).

Electrons may be effectively injected by providing the electroninjection layer 15. Therefore, transferring electrons to the organiclight-emitting layer 14 becomes easy, and high-speed response of theorganic EL device may be ensured by providing the electron injectionlayer 15.

The organic EL device 106 of the fourth embodiment shown in FIG. 3 hasthe same configuration as the organic EL device 104 of the thirdembodiment, except for the insertion of the electron injection layer 15between the organic light-emitting layer 14 and the cathode layer 16.Accordingly, the following description is focused on the electroninjection layer 15 which is characteristic of the fourth embodiment.Other parts are the same as those in the first to the third embodimentsor the configurations known in the field of organic EL devices.

(1) Materials

The electron injection layer is preferably formed from an organiccompound or an inorganic compound. The use of an inorganic compoundproduces organic EL devices with better electron injection performancefrom a cathode layer and superior durability.

As preferable organic compounds, 8-hydroxyquinoline, oxadizole, andderivatives of these compounds, such as a metal chelate oxynoidecompound containing 8-hydroxyquinoline, can be given.

An insulating material or semiconductor are preferably used as aninorganic compound forming the electron injection layer. If the electroninjection layer is made from an insulator or a semiconductor, leakage ofcurrent may be effectively prevented, resulting in improvement inelectron injection performance.

One or more metal compounds selected from the group consisting of alkalimetal chalcogenides (oxides, sulfides, selenides, tellurides), alkalineearth metal chalcogenides, alkali metal halides, and alkaline earthmetal halides can be used as such an insulator. If the electroninjection layer is made from these alkali metal chalcogenides or thelike, electron injection performance may be further improved.

As specific examples of preferable alkali metal chalcogenides, Li₂O,LiO, Na₂S, Na₂Se, and NaO can be given. As preferable alkaline earthmetal chalcogenides, for example, CaO, BaO, SrO, BeO, BaS, and CaSe canbe given. LiF, NaF, KF, LiCl, NaCl, KCl, NaCl, and the like can be givenas examples of preferable alkali metal halides. As specific examples ofpreferable alkaline earth metal halides, fluorides such as CaF₂, BaF₂,SrF₂, MgF₂, and BeF₂, and halides other than fluorides can be given.

As semiconductors which form the electron injection layer, oxides,nitrides, and oxynitrides containing at least one element selected fromBa, Ca, Sr, Yb, Al, Ga, In, Li, Na, Cd, Mg, Si, Ta, Sb, and Zn can begiven. These compounds can be used either individually or in combinationof two or more.

The inorganic compounds forming the electron injection layer arepreferably in the form of a microcrystalline or amorphous insulatingthin layer. If the electron injection layer is formed from theseinsulating thin layer, pixel deficiencies such as dark spots and thelike may be reduced because a uniform and homogeneous thin layer for theelectron injection layer may be obtained from these insulating thinlayer.

As such an inorganic compound, the above-mentioned alkali metalchalcogenides, alkaline earth metal chalcogenides, alkali metal halides,and alkaline earth metal halides can be given.

In addition, the electron injection layer may be made from a knownorganic compound having electron transport characteristics, or a mixtureof such an organic compound and an alkali metal, for example, a mixtureof the above-mentioned metal chelate compound containing 8-hydroxyquilyl(Alq) and Cs.

(2) Electron Affinity

It is desirable that the electron affinity of the electron injectionlayer in the first embodiment is in the range of 1.8 to 3.6 eV. If theelectron affinity is less than 1.8 eV, electron injection performancedecreases and the driving voltage increases, resulting in a loweredluminous efficiency; if the electron affinity is more than 3.6 eV, acomplex with a low luminous efficiency tends to be produced and ablocking junction may occur.

More preferable range of the electron affinity of the electron injectionlayer is therefore from 1.9 to 3 eV, and the range from 2 to 2.5 eV isideal.

In addition, it is desirable that the difference between the electronaffinity of the electron injection layer and that of the organiclight-emitting layer be 1.2 eV or less, and more preferably 0.5 eV orless. The smaller the difference in the electron affinity, the easierthe electron injection from the electron injection layer into theorganic light-emitting layer, ensuring a high-speed response of theorganic EL device.

(3) Energy Gap

It is desirable that the energy gap (bandgap energy) of the electroninjection layer in the first embodiment be 2.7 eV or more, and morepreferably 3.0 eV or more.

If the energy gap is greater than a prescribed value, 2.7 eV or more forexample, positive holes move to the electronic injection layer throughan organic light-emitting layer only with difficulty. The recombiningefficiency of positive holes and electrons is thus improved, resultingin an increase in the luminous brightness of the organic EL device andavoiding the case in which the electron injection layer itself emitslight.

(4) Configuration

Next, the configuration of the electron injection layer made from aninorganic compound will be described. There is no specific limitation tothe configuration of the electron injection layer. Either a mono-layerconfiguration or a multi-layer (two or more layers) configuration isacceptable.

Although the thickness of the electron injection layer is notspecifically restricted, this thickness is preferably in the range of0.1 nm to 1,000 nm, for example. If the thickness of the electroninjection layer made from an inorganic compound is less than 0.1 nm, theelectron injection force may decrease or the mechanical strength may beimpaired. If the thickness of the electron injection layer made from aninorganic compound is more than 1,000 nm, resistance is too high so thatit may be difficult for the organic EL device to exhibit a high-speedresponse and may take a long time to form the layers. Therefore, thethickness of the electron injection layer made from an inorganiccompound is more preferably from 0.5 to 100 nm, and still morepreferably from 1 to 50 nm.

(5) Method of Forming

Next, methods of forming the electron injection layer will be explained.The method of forming the electron injection layer is not specificallylimited inasmuch as a thin layer with a uniform thickness is obtained.For example, a vacuum deposition method, spin coating method, castingmethod, LB method, sputtering method, and the like can be employed.

(Fifth Embodiment)

A fifth embodiment of the present invention will be explained withreference to FIGS. 4 to 6. The method of the fifth embodiment ensuresproduction of a thin inorganic layer with a uniform ratio of componentseven if a plurality of inorganic compounds is used. This consequentlyprovides efficient method of manufacture of organic EL devicesexhibiting high luminous brightness at a low driving voltage and havingexcellent durability.

Specifically, a first feature of the fifth embodiment is forming aninorganic thin layer by using a specific target and a radio frequencymagnetron sputtering method.

A second feature of the fifth embodiment is in the use of a plurality oforganic light-emitting materials. For example, an organic light-emittinglayer with a uniform ratio of components may be obtained by using aplurality of organic light-emitting materials and a rotation vapordeposition method. Such an organic light-emitting layer ensuresefficient manufacture of organic EL devices exhibiting high luminousbrightness at a low driving voltage, and having excellent durability.

A third feature of the fifth embodiment is providing a vacuum vessel forthe radio frequency magnetron sputtering operation and another vacuumvessel for the vacuum deposition operation, and connecting the twovacuum vessels in advance for a continuous operation, wherein, after thevacuum deposition operation, the material is transferred to the vacuumvessel for the radio frequency magnetron sputtering method using acarriage means.

In explaining the method of manufacture according to the fifthembodiment, the organic EL device with the same configuration as thatused in the fourth embodiment is used for convenience.

The following layers are prepared using the manufacturing method of thefifth embodiment. The method of manufacturing each layer is as follows.

Anode layer: A radio frequency magnetron sputtering method

Inorganic thin layer: A radio frequency magnetron sputtering method

Positive hole transport layer: A vacuum deposition method

Organic light-emitting layer: A vacuum deposition method

Electron injection layer: A vacuum deposition method

Cathode layer: A vacuum deposition method

(1) Formation of Anode Layer and Inorganic Thin Layer

In forming an anode layer and an inorganic thin layer using the radiofrequency magnetron sputtering method, it is desirable to use a targetwhich consists of the inorganic compounds of group A and group B.

Specifically, the target contains at least the inorganic compounds ofgroup A and group B in a prescribed ratio, and is preferably prepared byhomogeneously mixing the raw materials (average particles diameter: 1μm) using a solution method (a coprecipitation method) (concentration:0.01 to 10 mol/l, solvent: polyhydric alcohol, etc., precipitationagent: potassium hydroxide, etc.) or a physical mixing method (stirrer:a ball mill, bead mil, etc., mixing time: 1 to 200 hours), followed bysintering (temperature: 1,200 to 1,500° C., time: 10 to 72 hours,preferably, 24 to 48 hours) and molding (press molding, HIP molding,etc.).

The targets obtained by these methods have uniform characteristics. Whenmolding, the preferable temperature is raised at a rate of 1 to 50° C.per minute.

Because the ratio of components and the like is adjusted only by thesputtering conditions, the inorganic compounds of group A and group Bcan also be sputtered separately.

Although the conditions of radio frequency magnetron sputtering are notspecifically restricted, sputtering is preferably performed in an inertgas such as argon under vacuum of 1×10⁻⁷ to 1×10⁻³ Pa, a layer formingspeed of 0.01 to 50 nm/second, and a substrate temperature of −50° C. to300° C. These conditions of sputtering ensures production of aninorganic thin layer having a precise and uniform thickness.

(2) Formation of Organic Light-Emitting Layer

A method of forming an organic light-emitting layer by simultaneousvaporization of different vapor deposition materials will now bedescribed referring to FIGS. 4 and 5. Specifically, the method using avacuum deposition apparatus 201, for example, is characterized byproviding a rotation axis line 213A passing through the geometricalcenter of the substrate 203 around which it is rotated, arranging vapordeposition material containers 212A to 212F at positions apart from therotation axis line 213A of the substrate 203, and causing the differentvapor deposition materials to simultaneously vaporize from the vapordeposition material containers 212A to 212F arranged opposingly to thesubstrate 203 while rotating the substrate 203 around a rotation axis213.

Vacuum Deposition Apparatus

The vacuum deposition apparatus 201 shown in FIGS. 4 and 5 has a vacuumvessel 210, a substrate holder 211 installed in the upper portion of thevacuum vessel 210 for securing the substrate 203, and a plurality of(six) vapor deposition material containers 212A to 212F for -fillingvapor deposition materials, which are opposingly arranged below thesubstrate holder 211. This vacuum vessel 210 is designed so that anexhaust means (not shown in the drawing) can maintain the internalpressure at a prescribed reduced pressure. Although six vapor depositionmaterials are shown in the drawing, the number is not necessarilylimited to six. Five or less or seven or more materials are acceptable.

The substrate holder 211 has a holder section 215 which supports theperipheral portion of the substrate 203 and holds the substrate 203horizontally in the vacuum vessel 210. A rotation axis member 213 forrotating the substrate 203 is provided in the vertical directionupwardly in the center of the substrate holder 211. A motor 214 which isa rotation driving means is connected to the rotation axis member 213.The substrate 203 held in the substrate holder 211 is rotated togetherwith the substrate holder 211 around the rotation axis member 213 by therotational movement action of the motor 214. The rotation axis line 213Aextending from the rotation axis member 213 is set in the verticaldirection in the center of the substrate 203.

Method of Forming

Next, a method of forming an organic light-emitting layer 12 on thesubstrate 203 from two kinds of organic light-emitting materials (a hostmaterial and a doping material) by using the vacuum deposition apparatus201 will be specifically explained.

First, a square substrate 203 shown in FIG. 5 is caused to engage theholding section 215 of the substrate holder 211 and is horizontallymaintained.

In forming the organic light-emitting layer 12, the host material anddoping material are filled into each of the two vapor depositionmaterial containers 212B and 212C which are located in juxtaposition ona virtual circle 221 shown in FIG. 4, and pressure in the vacuum vessel210 is reduced to a vacuum of a prescribed level, 1.0×10⁻⁴ Torr(133×10⁻⁴ Pa), for example, using an exhaust means.

Next, the vapor deposition material containers 212B and 212C are heatedto cause the host material and doping material to simultaneouslyvaporize from the respective containers. At the same time, a motor 214is driven to rotate the substrate 203 at a prescribed rate, 1 to 100 rpm(revolution per minute) for example, around the rotation axis line 213A.The organic light-emitting layer 12 is formed by causing the hostmaterial and doping material to deposit while rotating the substrate 203in this manner.

Because the vapor deposition material containers 212B and 212C areprovided in the positions at a prescribed distance “M” from the rotationaxis line 213A of the substrate 203 in the horizontal direction as shownin the FIG. 5, it is possible to regularly change the angle of incidenceto the substrate 203 of the vapor deposition materials such as the hostmaterial and doping material by rotating the substrate 203.

Therefore, it is possible to cause the vapor deposition materials tobecome uniformly attached to the substrate 203, thereby ensuringformation of a thin layer with a homogeneous compositionalconcentration, for instance, with a concentration fluctuation of ±10%(mol conversion).

Because the substrate 203 need not be revolved in performing the vapordeposition, space and equipment for this purpose are unnecessary, thusenabling an economical layer-forming operation in minimum space. Here,to revolve a substrate means to cause the substrate to rotate around anaxis which is some distance from its geometric center. This requires alarger space than the case where the substrate rotates around itsgeometrical center.

Arrangement of Vapor Deposition Material Containers (1)

There are no specific limitations to the configuration of the substrate203 in carrying out the simultaneous vapor deposition. In the case wherethe substrate 203 is a plate as shown in FIG. 4, for example, it isdesirable to arrange a plurality of vapor deposition material containers212A to 212F along the perimeter of a virtual circle 221 around therotation axis line 213A of the substrate 203, so that the relationship“M>(½)×L” is satisfied, wherein “M” is the diameter of the virtualcircle 221 and “L” is the length of one side of the substrate 203. Whenthe substrate 203 has sides with different lengths, “L” indicates thelength of the longest side.

This arrangement ensures easy control of the compositional ratio of thevapor deposition materials because the vapor deposition materials from aplurality of containers 212A to 212F become attached to the substrate203 at the same angle of incidence.

In addition, because this arrangement ensures vaporization of the vapordeposition materials at a certain angle of incidence to the substrate203 and prevent the vapor deposition materials from evaporating at rightangles, uniformity of the compositional ratio in the formed layer may befurther improved.

Arrangement of Vapor Deposition Material Containers (2)

In performing the method of manufacturing of the fifth embodiment, aplurality of vapor deposition material containers 212A to 212F isarranged along the perimeter of a virtual circle 221 around the rotationaxis line 213A of the substrate 203 as shown in FIG. 4. In thisinstance, it is desirable that the vapor deposition material containers212A to 212F are arranged with an angle of 360°/n from the center of thevirtual circle 221, wherein “n” indicates the number of vapor depositionmaterial containers. For example, when six vapor deposition materialcontainers 212 are provided, it is suitable to place the containers withan angle of 60° from the center of the virtual circle 221.

When arranged in this manner, a plurality of vapor deposition materialsis successively superposed on each section of the substrate 203.Therefore, a thin layer with a content of components regularly differingin the direction of the thickness of the layer is easily prepared.

Layer Composition

Next, uniformity of the composition in the organic light-emitting layerformed by the above-mentioned simultaneous vapor deposition method willbe discussed in detail. As an example, a thin layer (an electronicinjection layer) with a thickness of 1,000 Å (a prescribed value) isprepared by simultaneous vapor deposition using Alq as a host materialand Cs as a doping material while rotating the substrate 203 shown inFIG. 6 at 5 rpm under the following conditions.

Cs is used here to increase the electronic conduction of Alq, not as aconventional doping agent to emit light. The following example is givenas a typical method of forming uniform layer. Although Cs itself has nolight-emitting function, the example is applicable when Cs is replacedwith a doping agent with a light-emitting function.

Alq deposition rate 0.1 to 0.3 nm/s Cs deposition rate 0.1 to 0.3 nm/sAlq/Cs thickness 1,000 Å (a prescribed value)

The thickness of the resulting thin layer at measuring points (4A to 4M)on a glass substrate 203 shown in FIG. 6 was measured using atracer-type thickness meter. The composition ratio (the atomic ratio)Cs/Al (Al in Alq) at the above measuring points (4A to 4M) was alsomeasured by using an X-ray photoelectron spectrometer (XPS). Themeasuring points (4A to 4M) on a glass substrate 203 shown in FIG. 6were determined by dividing the substrate 203 into 16 squares having anequal side length of “P” is 50 mm and arbitrarily selecting the corners(13 corners) of these squares. The results are shown in Table 1.

TABLE 1 Measuring point Thickness (Å) Cs/Al 4A 1,053 1.0 4B 1,035 1.0 4C1,047 1.0 4D 1,088 1.1 4E 1,091 1.0 4F 1,093 1.1 4G 1,082 1.1 4H 1,0751.0 4I 1,082 1.1 4J 1,065 1.1 4K 1,010 1.0 4L 1,008 1.0 4M 1,025 1.0

As a reference example, a thin layer with a thickness of 1,000 Å (aprescribed value) was prepared under the same vapor depositionconditions as in the above simultaneous vapor deposition, except thatthe substrate 203 was not rotated. The thickness and atomic ratio Cs/Al(Al in Alq) of the resulting thin layer at measuring points (4A to 4M)were measured. The results are shown in Table 2.

TABLE 2 Measuring point Thickness (Å) Cs/Al 4A 895 0.6 4B 941 1.1 4C 8841.1 4D 911 0.7 4E 922 1.1 4F 1,022   0.8 4G 919 1.2 4H 1,015   1.3 4I1,067   0.7 4J 908 1.2 4K 895 0.5 4L 920 1.0 4M 950 1.1

As clear from these results, the minimum thickness and the maximumthickness of the layer prepared by the simultaneous vapor depositionmethod at the measuring points (4A to 4M) on the surface of thesubstrate 203 were respectively 1,008 Å (100.8 nm) and 1,093 Å (109.3nm). Thus, the layer was confirmed to have a very uniform thickness,with a maximum thickness difference of as small as 85 Å, and also tohave a very homogeneous composition, with an atomic ratio Cs/Al withinthe range of 1.0 to 1.1.

On the other hand, the layer prepared by a method differing from theabove simultaneous vapor deposition method had a thickness whichfluctuated from 884 Å to 1,067 Å at the measuring points (4A to 4M) onthe substrate 203. The atomic ratio Cs/Al also showed fluctuationsranging from 0.6 to 1.3.

EXAMPLES Example 1

(1) Preparation For Manufacturing Organic EL Device

Before manufacturing the organic EL device of Example 1, a transparentelectrode layer with a thickness of 75 nm was formed from ITO as ananode layer on a transparent glass substrate with a dimension ofthickness:1.1 mm×length:25 mm×width:75 mm. The glass substrate and theanode layer are collectively called a substrate in the followingdescription. This substrate was ultrasonically washed in isopropylalcohol, dried in a nitrogen gas atmosphere, and washed for 10 minutesusing UV (ultraviolet radiation) and ozone.

(2) Formation of Inorganic Thin Layer

Next, the substrate on which an anode layer has been formed was placedin a vacuum vessel for common use as a radio frequency sputteringapparatus and a vacuum deposition apparatus. A target consisting of tinoxide and ruthenium oxide (at a ratio of 10:1) to form an inorganic thinlayer was installed in the vacuum vessel. After reducing the pressure inthe vacuum vessel to 1×10⁻⁵ Torr, a mixed gas of oxygen and argon wasintroduced. An inorganic thin layer with a thickness of 10 nm was formedby sputtering at an output of 100 W and a substrate temperature of 200°C.

(3) Formation of Organic Light-Emitting Layer

Then, switching the function of the vessel from the radio frequencysputtering apparatus to the vacuum deposition apparatus, the substratewas inserted in the substrate holder in the vacuum vessel of the vacuumdeposition apparatus, as shown in FIG. 5. The vapor deposition materialcontainer 212B was filled with a compound described by the formula (6)(abbreviated as DPVTP) as an organic light-emitting material, thecontainer 212C was filled with a compound described by the formula (24)(abbreviated as DPAVBi) as another organic light-emitting material, thecontainer 212D was filled with Alq which forms an electronic injectionlayer, the container 212E was filled with a metal (Al) which forms partof a cathode layer, and the container 212F was filled with another metal(Li) which forms part of the cathode layer.

Next, after reducing the pressure in the vacuum vessel to 1×10⁻⁶ Torr orless, an organic light-emitting layer, an electron injection layer, anda cathode layer were sequentially laminated on the substrate consistingof an anode layer and an inorganic thin layer, thereby obtaining anorganic EL device. The same vacuum conditions were constantly maintainedall through the operation from formation of the organic light-emittinglayer through the formation of the cathode layer.

More specifically, DPVTP and DPAVBi were simultaneously vaporized fromthe vapor deposition material containers 212B and 212C under thefollowing conditions to form an organic light-emitting layer on aninorganic thin layer.

DPVTP vaporization rate 0.5 nm/s DPAVBi vaporization rate 0.1 nm/sDPVTP/DPAVBi thickness 40 nm

The method of the fifth embodiment was followed in simultaneouslydepositing vaporized DPVTP and DPAVBi. Specifically, in forming theorganic light-emitting layer, the vapor deposition material containers212B and 212C were respectively arranged at positions at a distance fromthe rotation axis line of the substrate of 30 mm in the horizontaldirection, and the containers were heated in this positional arrangementto simultaneously vaporize DPVTP and DPAVBi, while rotating thesubstrate around the rotation axis at 5 rpm.

Next, Alq was vaporized from the vapor deposition material containers212D under the following conditions to form an An electron injectionlayer on the organic light-emitting layer.

Alq vaporization rate 0.2 nm/s Alq thickness 5 nm

Finally, Al and Li were vaporized respectively from the vapor depositionmaterial containers 212E and 212F to form a cathode layer on theelectron injection layer, thereby providing an organic EL device.

Al vaporization rate 1 nm/s Li vaporization rate 0.01 nm/s Al/Lithickness 200 nm

(4) Evaluation of Organic EL Device

A DC voltage of 8V was applied between the cathode layer (minus (−)electrode) and the anode layer (plus (+) electrode) of the resultingorganic EL device. At this time, the current density was 1.5 mA/cm² andthe luminous brightness was 127 nit (cd/m²). In addition, the emittedcolor was confirmed to be blue. Furthermore, durability was evaluated bydriving at a constant current of 10 mA/cm², to confirm that there was nooccurrence of a leakage current after operating for 1,000 hours andlonger.

TABLE 3 Example 1 2 3 4 Anode layer ITO ITO ITO ITO material Ip(eV) 5.05.0 5.0 5.0 Thickness (nm) 75 75 75 75 Inorganic thin layer Sn oxide/SiO_(x)/ GeO_(x)/ SiO_(x)/Ru oxide material Ru oxide Ru oxide Ru oxide(10/1.5) Ip(eV) 5.53 5.53 5.47 5.54 Thickness (nm) 1 2 1 5Light-emitting layer DPVTP/ DPVTP/ DPVTP/ DPVTP/ material DPAVBi DPAVBiDPAVBi DPAVBi Thickness (nm) 40 40 40 40 Electron injection Alq Alq Alqlayer material Thickness (nm) 5 5 5 Cathode layer Al/Li Al/Li Al/LiAl/Li material Thickness (nm) 200 200 200 200 Current density 1.5 1.71.3 1.0 (mA/cm²) Luminous 127 137 114 130 brightness (cd/m²) Durability1,000 1,000 1,000 1,000 hours or hours or hours or hours or longerlonger longer longer Transmittance (%) 83 83 82 83

TABLE 4 Comparative Example 1 2 3 Anode layer material ITO ITO ITOIp(eV) 5.0 5.0 5.0 Thickness (nm) 75 75 75 Inorganic thin layer Sn oxideRu oxide material Ip(eV) 4.8 5.4 Thickness (nm) 10 10 Light-emittinglayer DPVTP/ DPVTP/ DPVTP/ material DPAVBi DPAVBi DPAVBi Thickness (nm)40 40 40 Electron injection layer material Alq Alq Alq Thickness (nm) 55 5 Cathode layer material Al/Li Al/Li Al/Li Thickness (nm) 200 200 200Current density 2.2 0.9 0.6 (mA/cm²) Luminous brightness 127 68 20(cd/m²) Durability Less than 1,000 hours 1,000 hours 1,000 hours orlonger or longer Transmittance (%) 87 80 53

Examples 2 to 4

In Examples 2 to 4, organic EL devices were prepared in the same manneras in Example 1, except for changing the types of inorganic compoundsand the amounts of the components as shown in Table 3. Luminousbrightness and the like were evaluated.

As shown in Table 3, the ionization potential of the inorganic thinlayer of each Example was 5.4 eV or more. This is presumed to be due toan intermediate level formed in the inorganic thin layer. The ionizationenergy of DPVTP which is an organic light-emitting material was 5.9 eV,confirming that the value is greater than the intermediate level (anenergy value) of the inorganic thin layer.

Comparative Example 1

The organic EL device of Comparative Example 1 was prepared in the samemanner as in Example 1, except that an inorganic thin layer was notformed. A DC voltage of 10V was applied to the resulting organic ELdevice in the same manner as in Example 1. As a result, although theorganic EL device emitted blue light, the current density was 2.2 mA/cm²and the luminous brightness was 127 nit (cd/m²). In addition, when theorganic EL device was operated at a constant current of 10 mA/cm², aleakage current occurred before operating for 1,000 hours and theorganic EL device ceased to emit light.

Comparative Example 2

The organic EL device of Comparative Example 2 was the same as that ofExample 1, except that an inorganic thin layer was formed using only tinoxide. A DC voltage of 10V was applied to the resulting organic ELdevice in the same manner as in Example 1. This driving voltage was 2Vhigher than that used in Examples 1 to 4 (8V).

As a result, although the organic EL device emitted blue light, thecurrent density was 0.9 mA/cm² and the luminous brightness was 68 nit(cd/m²). The organic EL device was operated at a constant current of 10mA/cm² in the same manner as in Example 1 to confirm that a leakagecurrent did not occur after operating for 1,000 hours.

Comparative Example 3

The organic EL device of Comparative Example 3 was the same as that ofExample 1, except that an inorganic thin layer was formed using onlyaluminum nitride. A DC voltage of 10V was applied to the resultingorganic EL device in the same manner as in Example 1. This drivingvoltage was 2V higher than that used in Examples 1 to 4 (8V).

As a result, although emission of blue light was confirmed, the currentdensity was 0.6 mA/cm² and the luminous brightness was 20 nit (cd/m²).The organic EL device was operated at a constant current of 10 mA/cm² inthe same manner as in Example 1 to confirm that a leakage current didnot occur after operating for 1,000 hours.

Examples 5 to 10

In Examples 5 to 10, organic EL devices were prepared in the same manneras in Example 1, except for changing the materials for forming anodelayers and inorganic thin layers as shown in Table 5. Luminousbrightness and the like were evaluated.

In Example 9, nitrogen gas was added to a mixture of argon gas andoxygen gas. Then the resulting gas mixture was used afterplasma-treatment.

In addition, in Example 10 a mixture of argon gas and nitrogen gas wasused after plasma-treatment. The results are shown in Table 5, whereinIZO means non-crystalline indium zinc oxide.

TABLE 5 Example 5 6 7 8 9 10 Anode layer material IZO IZO IZO IZO IZOIZO Ip(eV) 5.2 5.2 5.2 5.2 5.2 5.2 Thickness (nm) 80 85 90 80 85 85Inorganic thin layer Zn oxide Zn sulfide Al oxide Mg oxide Si oxynitrideAl nitride material Pd oxide Pd oxide Re oxide Ru oxide Pd oxide Pdoxide Ip(eV) 5.6 5.6 5.5 5.5 5.6 5.6 Thickness (nm) 80 85 90 80 85 85Light-emitting layer DPVTP/ DPVTP/ DPVTP/ DPVTP/ DPVTP/ DPVTP/ materialDPAVBi DPAVBi DPAVBi DPAVBi DPAVBi DPAVBi Thickness (nm) 80 80 80 80 8080 Electron injection Alq Alq Alq Alq Alq Alq layer material Thickness(nm) 5 5 5 5 5 5 Cathode layer material Al/Li Al/Li Al/Li Al/Li Al/LiAl/Li Thickness (nm) 100 100 100 100 100 100 Current density (mA/cm²)1.6 1.4 1.8 1.8 1.7 1.8 Luminous brightness 156 145 133 122 144 155(cd/m²) Durability 1,000 hours 1,000 hours 1,000 hours 1,000 hours 1,000hours 1,000 hours or longer or longer or longer or longer or longer orlonger Transmittance (%) 88 85 86 85 88 88

Example 11

(1) Preparation For Manufacturing Organic EL Device

(Preparation of Target)

A mixture of indium oxide powder and iridium oxide powder (averageparticle diameter: 1 μm or less) was placed in a wet-type ball mill inthe amounts so that the molar ratio of Ir/(In+Ir) is 0.02 and pulverizedfor 72 hours. The resulting pulverized material was granulated andpress-molded to form a disk with a diameter of 4 inch and a thickness of5 mm. The disk was sintered at a temperature of 1,400° C. for 36 hoursto obtain a target 1 for an anode layer. A target 2 for an inorganicthin layer consisting of tin oxide and ruthenium oxide (atomicratio=10:1) was prepared in the same manner.

(2) Formation of Anode Layer

Next, a transparent glass substrate with a dimension of thickness:1.1mm×length:25 mm×width:75 mm and the target 1 were placed in a vacuumvessel for common use as a radio frequency sputtering apparatus and avacuum deposition apparatus. The radio frequency sputtering apparatuswas operated to form a transparent electrode layer with a thickness 75nm as an anode layer. After reducing the pressure in the vacuum vesselto 3×10⁻¹ Pa, a mixed gas of oxygen and argon was fed. A transparentelectrode layer was formed by sputtering in this atmosphere at an outputof 100 W and a substrate temperature of 25° C. for 14 minutes.

The glass substrate and the anode layer are collectively called asubstrate in the following description. This substrate wasultrasonically washed in isopropyl alcohol, dried in a nitrogen gasatmosphere, and washed for 10 minutes using UV (ultraviolet radiation)and ozone. The ionization potential of the anode layer in the substratewas measured using “AC-1” (Riken Instrument Co., Ltd.) to find thationization potential was 5.54 eV. In addition, the light transmittance(wavelength 550 nm) of the substrate from which the anode layer wasformed was measured to confirm that the light transmittance was 80%.

(3) Formation of Inorganic Thin Layer

The substrate on which an anode layer has been formed was placed in avacuum vessel for common use as a radio frequency sputtering apparatusand a vacuum deposition apparatus. A target 2 consisting of tin oxideand ruthenium oxide was installed in the vacuum vessel. After reducingthe pressure in the vacuum vessel to 1×10⁻⁶ Torr, an inorganic thinlayer with a thickness of 10 nm was formed by sputtering at an output of100 W and a substrate temperature of 200° C.

(4) Formation of Organic Light-Emitting Layer

Then, switching the function of the vessel from the radio frequencysputtering apparatus to the vacuum deposition apparatus, the substratewas inserted in the substrate holder in the vacuum vessel of the vacuumdeposition apparatus, as shown in FIG. 4. The vapor deposition materialcontainer 212B was filled with a compound DPVTP which forms part of anorganic light-emitting layer, the container 212C was filled with DPAVBiwhich is another compound forming the organic light-emitting layer, thecontainer 212D was filled with an organic compound Alq which forms anelectronic injection layer, the container 212E was filled with a metal(Al) which forms part of a cathode layer, and the container 212F wasfilled with another metal (Li) which forms part of the cathode layer.

Next, after reducing the pressure in the vacuum vessel to 1×10⁻⁶ Torr orless, an organic light-emitting layer, an electron injection layer, anda cathode layer were sequentially laminated on the substrate consistingof an anode layer and an inorganic thin layer, thereby obtaining anorganic EL device.

The same vacuum conditions have been constantly maintained all throughthe operation from formation of the organic light-emitting layer throughthe formation of the cathode layer. More specifically, DPVTP and DPAVBiwere simultaneously vaporized from the vapor deposition materialcontainers 212B and 212C under the following conditions to form anorganic light-emitting layer on an inorganic thin layer.

DPVTP vaporization rate 0.5 nm/s DPAVBi vaporization rate 0.1 nm/sDPVTP/DPAVBi thickness 40 nm

The method of the fourth embodiment was followed in carrying out thesimultaneous deposition. Specifically, in forming the organiclight-emitting layer, the vapor deposition material containers 212B and212C were respectively arranged at positions apart from the rotationaxis line of the substrate by 30 mm in the horizontal directions, andthe containers were heated in this positional arrangement tosimultaneously vaporize DPVTP and DPAVBi, while rotating the substratearound a rotation axis at 5 rpm.

Next, Alq was vaporized from the vapor deposition material containers212D under the following conditions to form an electron injection layeron the organic light-emitting layer.

Alq vaporization rate 0.2 nm/s Alq thickness 5 nm

Finally, Al and Li were vaporized respectively from the vapor depositionmaterial containers 212E and 212F to form a cathode layer on theelectron injection layer, thereby obtaining an organic EL device.

Al vaporization rate 1 nm/s Li vaporization rate 0.01 nm/s Al/Lithickness 200 nm

(5) Evaluation of Organic EL Device

A DC voltage of 8V was applied between the cathode layer (minus (−)electrode) and the anode layer (plus (+) electrode) of the resultingorganic EL device. At this time, the current density was 1.1 M/cm² andthe luminous brightness was 89 nit (cd/m²). In addition, the emittedcolor was confirmed to be blue. Furthermore, durability was evaluated bydriving at a constant current of 10 mA/cm², to find that there was nooccurrence of a leakage current after the operation of 1,000 hours andlonger. The results are shown in Table 6.

Example 12

An organic EL device was prepared in the same manner as in Example 11except that a target 3 consisting of indium oxide, tin oxide, zincoxide, and molybdenum oxide, with a molar ratio In/(In+Sn+Zn)=0.6,Sn/(In+Sn+Zn)=0.3, Zn/(In+Sn+Zn)=0.1, and Mo/(In+Sn+Zn+Mo)=0.02, wasused instead of the target 1 used in Example 11. The ionizationpotential of the anode layer was 5.46 eV.

A DC voltage of 8V was applied to the resulting organic EL devicebetween the electrodes to confirm that the current density was 1.4mA/cm² and the luminous brightness was 108 nit (cd/m²). In addition, theemitted color was confirmed to be blue.

Example 13

An organic EL device was prepared in the same manner as in Example 11except that a target 4 consisting of indium oxide, tin oxide, zincoxide, and palladium oxide, with a molar ratio In/(In+Sn+Zn)=0.6,Sn/(In+Sn+Zn)=0.3, Zn/(In+Sn+Zn)=0.1, and Pd/(In+Sn+Zn+Pd)=0.02, wasused instead of the target 1 used in Example 11. The ionizationpotential of the anode layer was 5.60 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 1.4 mA/cm² and the luminous brightness was 108nit (cd/m²). In addition, the emitted color was confirmed to be blue.

Example 14

An organic EL device was prepared in the same manner as in Example 11except that a target 5 consisting of indium oxide, tin oxide, zincoxide, and rhenium oxide, with a molar ratio In/(In+Sn+Zn)=0.6,Sn/(In+Sn+Zn)=0.3, Zn/(In+Sn+Zn)=0.1, and Re/(In+Sn+Zn+Re)=0.02, wasused instead of the target 1 used in Example 11. The ionizationpotential of the anode layer was 5.52 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 1.2 mA/cm² and the luminous brightness was 94nit (cd/m²). In addition, the emitted color was confirmed to be blue.

TABLE 6 Example 11 12 13 14 Anode layer material In oxide/ In oxide/ Inoxide/ In oxide/ Ir oxide Sn oxide/ Sn oxide/ Sn oxide/ Zn oxide/ Znoxide/ Zn oxide/ Mo oxide/ Pd oxide/ Re oxide/ Ip(eV) 5.54 5.46 5.605.52 Thickness (nm) 75 75 75 75 Light-emitting layer DPVTP/ DPVTP/DPVTP/ DPVTP/ material DPAVBi DPAVBi DPAVBi DPAVBi Thickness (nm) 40 4040 40 Electron injection layer material Alq Alq Alq Alq Thickness (nm) 55 5 5 Cathode layer material Al/Li Al/Li Al/Li Al/Li Thickness (nm) 200200 200 200 Current density 1.2 1.1 1.4 1.2 (mA/cm²) Luminous brightness97 89 108 94 (cd/m²) Durability 1,000 1,000 1,000 1,000 hours hourshours hours or longer or longer or longer or longer Transmittance (%) 8079 77 81

Examples 15 to 20

Organic EL devices were prepared in the same manner as in Example 11,except for using the targets shown in Table 7 instead of the target 1 inExample 11, the compound described by the formula (8) (hereinafterabbreviated as DPVDPAN) as an light-emitting layer material, and thecompound described by the formula (23) (hereinafter abbreviated as PAVB)as a doping material to be added to the light-emitting layer. Theresults are shown in Table 7.

As clear from the results, although the ionization potentials of theanode layers coincided with the work functions, the values were greaterthan 5.4 eV in all Examples.

Except for oxides of In an Sn of Example 20, these anode layers wereconfirmed to be amorphous by the X-ray diffraction measurement.

Moreover, the surface roughness of the anode layers was measured byusing a surface roughness meter to confirm that the mean value of thesquares was less than 10 nm, confirming that the surfaces were and verysmooth.

However, the anode layer of Example 20, which is a mixture of crystalsand amorphous materials, exhibited surface roughness of less than 35 nm.The anode partly short-circuited, although a current could flow at a lowvoltage.

TABLE 7 Example 15 16 17 18 19 20 Anode layer material In oxide In oxideIn oxide In oxide In oxide In oxide Zn oxide Zn oxide Zn oxide Zn oxideZn oxide Sn oxide Pd oxide Ir oxide Re oxide V oxide Mo oxide Mo oxideB/(A + B + C) 0.25 0.25 0.25 0.25 0.25 0.1 C/(A + B + C) 0.03 0.03 0.030.03 0.03 0.03 Ip(eV) 5.6 5.52 5.51 5.46 5.43 5.41 Thickness (nm) 80 8590 80 85 85 Inorganic thin layer Zn oxide Zn sulfide Al oxide Mg oxideSi oxynitride Al nitride material Pd oxide Pd oxide Re oxide Ru oxide Pdoxide Pd oxide Ip(eV) 5.6 5.6 5.5 5.5 5.6 5.6 Thickness (nm) 80 85 90 8085 85 Light-emitting layer DPVDPAN/ DPVDPAN/ DPVDPAN/ DPVDPAN/ DPVDPAN/DPVDPAN/ material PAVB PAVB PAVB PAVB PAVB PAVB Thickness (nm) 80 80 8080 80 80 Electron injection Alq/Cs Alq/Cs Alq/Cs Alq/Cs Alq/Cs Alq/Cslayer material Thickness (nm) 5 5 5 5 5 5 Cathode layer material Al AlAl Al Al Al Thickness (nm) 100 100 100 100 100 100 Current density(mA/cm²) 1.4 1.5 1.5 1.6 1.8 2.8 Luminous brightness 156 135 143 142 144140 (cd/m²) Durability 1,000 hours 1,000 hours 1,000 hours 1,000 hours1,000 hours 1,000 hours or longer or longer or longer or longer orlonger or longer Transmittance (%) 82 75 76 85 85 78

In the Table 7, A indicates the number of mols of the anode layermaterial (indium oxide) in the first row; B indicates the number of molsof the anode layer material (zinc oxide) in the second row; and Cindicates the number of mols of the anode layer material (palladiumoxide) in the third row.

Example 21

An organic EL device was prepared in the same manner as in Example 11except that a target 6 consisting of indium oxide, tin oxide, zincoxide, and ruthenium oxide, with a molar ratio In/(In+Sn+Zn)=0.6,Sn/(In+Sn+Zn)=0.3, Zn/(In+Sn+Zn)=0.1, and Ru/(In+Sn+Zn+Ru)=0.02, wasused instead of the target 1 used in Example 11. The ionizationpotential of the anode layer was 5.52 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 1.2 mA/cm² and the luminous brightness was 95nit (cd/m²). In addition, the emitted color was confirmed to be blue.

Example 22

An organic EL device was prepared in the same manner as in Example 11except that a target 7 consisting of indium oxide, tin oxide, zincoxide, and vanadium oxide, with a molar ratio In/(In+Sn+Zn)=0.6,Sn/(In+Sn+Zn)=0.3, Zn/(In+Sn+Zn)=0.1, and V/(In+Sn+Zn+V)=0.02, was usedinstead of the target 1 used in Example 11. The ionization potential ofthe anode layer was 5.45 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 1.1 mA/cm² and the luminous brightness was 84nit (cd/m²). In addition, the emitted color was confirmed to be blue.

Example 23

An organic EL device was prepared in the same manner as in Example 11except that a target 8 consisting of indium oxide, tin oxide, zincoxide, and iridium oxide, with a molar ratio In/(In+Sn+Zn)=0.6,Sn/(In+Sn+Zn)=0.3, Zn/(In+Sn+Zn)=0.1, and Ir/(In+Sn+Zn+Ir)=0.02, wasused instead of the target 1 used in Example 11. The ionizationpotential of the anode layer was 5.49 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 1.2 mA/cm² and the luminous brightness was 93nit (cd/m²). In addition, the emitted color was confirmed to be blue.

Example 24

An organic EL device was prepared in the same manner as in Example 11except that a target 10 consisting of indium oxide, zinc oxide, andcarbon, with a molar ratio In/(In+Zn)=0.78, Zn/(In+Zn)=0.12, andC/(In+Zn+C)=0.1, was used instead of the target 1 used in Example 11.The ionization potential of the anode layer was 5.31 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 1.4 mA/cm² and the luminous brightness was 120nit (cd/m²). In addition, the emitted color was confirmed to be blue.

Example 25

An organic EL device was prepared in the same manner as in Example 11except that a target 11 consisting of indium oxide, tin oxide, zincoxide, and silicon oxide, with a molar ratio In/(In+Sn+Zn)=0.6,Sn/(In+Sn+Zn)=0.2, Zn/(In+Sn+Zn)=0.1, and Si/(In+Sn+Zn+Si)=0.l, was usedinstead of the target 1 used in Example 11. The ionization potential ofthe anode layer was 5.26 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 1.1 mA/cm² and the luminous brightness was 90nit (cd/m²). In addition, the emitted color was confirmed to be blue.

Example 26

An organic EL device was prepared in the same manner as in Example 11except that a target 12 consisting of indium oxide, tin oxide, zincoxide, and carbon, with a molar ratio In/(In+Sn+Zn)=0.6,Sn/(In+Sn+Zn)=0.3, Zn/(In+Sn+Zn)=0.1, and C/(In+Sn+Zn+C)=0.02, was usedinstead of the target 1 used in Example 11. The ionization potential ofthe anode layer was 5.30 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 2.4 mA/cm² and the luminous brightness was 190nit (cd/m²). In addition, the emitted color was confirmed to be blue.

Comparative Example 4

An organic EL device was prepared in the same manner as in Example 11except that a target 9 consisting of indium oxide, tin oxide, and zincoxide, with a molar ratio In/(In+Sn+Zn)=0.6, Sn/(In+Sn+Zn)=0.3, andZn/(In+Sn+Zn)=0.1, was used instead of the target 1 used in Example 5.The ionization potential of the anode layer was 5.23 eV.

In the same manner as in Example 11, a DC voltage of 8V was applied tothe resulting organic EL device between the electrodes to confirm thatthe current density was 0.6 mA/cm² and the luminous brightness was 49nit(cd/m²). In addition, the emitted color was confirmed to be blue.

TABLE 8 Comparative Example Example 21 22 23 24 25 26 4 Anode layermaterial In oxide/ In oxide/ In oxide/ In oxide/ In oxide/ In oxide/ Inoxide/ Sn oxide/ Sn oxide/ Sn oxide/ Zn oxide/ Sn oxide/ Sn oxide/ Snoxide/ Zn oxide/ Zn oxide/ Zn oxide/ Carbon Zn oxide/ Zn oxide/ Znoxide/ Ru oxide/ V oxide/ Ir oxide/ Si oxide Carbon Ip(eV) 5.52 5.455.49 5.31 5.26 5.30 5.23 Thickness (nm) 75 75 75 75 75 75 75Light-emitting layer DPVTP/ DPVTP/ DPVTP/ DPVTP/ DPVTP/ DPVTP/ DPVTP/material DPAVBi DPAVBi DPAVBi DPAVBi DPAVBi DPAVBi DPAVBi Thickness (nm)40 40 40 40 40 40 40 Electron injection Alq Alq Alq Alq Alq Alq Alqlayer material Thickness (nm) 5 5 5 5 5 5 5 Cathode layer material Al/LiAl/Li Al/Li Al/Li Al/Li Al/Li Al/Li Thickness (nm) 200 200 200 200 200200 200 Current density 1.2 1.1 1.2 1.4 1.1 2.4 0.6 (mA/cm²) Luminousbrightness 95 84 93 120 90 190 49 (cd/m²) Durability 1,000 hours 1,000hours 1,000 hour 1,000 hours 1,000 hours 1,000 hours 1,000 hours orlonger or longer or longer or longer or longer or longer or longerTransmittance (%) 81 80 81 77 81 78 79

Industrial Application of the Invention

As described above in detail, according to the present invention even inthe case where an inorganic thin layer is provided in an organic ELdevice, an intermediate level for injection of electron charges may beformed in the inorganic thin layer without using a tunnel effect byforming the inorganic thin layer by a combination of several specificinorganic compounds, for example. Therefore, the present inventionprovides an organic EL device exhibiting superior durability, a lowdriving voltage, and high luminous brightness, and method of efficientlymanufacturing such an organic EL device.

What is claimed is:
 1. An organic electroluminescent device, comprising:a) an anode layer; b) an organic light-emitting layer; c) a cathodelayer; and; either or both of a first inorganic thin layer formedbetween the anode layer and the organic light-emitting layer, and asecond inorganic thin layer formed between the cathode layer and theorganic light-emitting layer, either or both of the first and secondinorganic thin layers consisting essentially of an oxide of Nb and atleast one compound selected from the following group A, group Aconsisting of chalcogenides and nitrides of Si, Ge, Sn, Pb, Ga, In, Zn,Cd, Mg, Al, Ba, K, Li, Na, Ca, Sr, Cs, and Rb.
 2. The organicelectroluminescent device of claim 1, wherein the compounds of group Aare selected from the group consisting of chalcogenides and nitrides ofSi, Ge, Sn, Zn, Cd, Al and Mg.
 3. The organic electroluminescent deviceof claim 1, wherein the content of the oxide of Nb is in the range of0.1 to 50 atomic % for 100 atomic % of the total of the first or secondinorganic thin layer.
 4. The organic electroluminescent device of claim1, wherein the thickness of the first or second inorganic thin layer is1 to 100 nm.
 5. The organic electroluminescent device of claim 1,wherein either or both of the first and second inorganic thin layersconsists of the oxide of Nb and the at least one compound selected fromthe group A.
 6. An organic electroluminescent device, comprising: a) ananode layer; b) an organic light-emitting layer; and c) a cathode layer;the anode layer, or the anode layer and the cathode layer, comprising anoxide of Nb and at least one compound selected from the following groupA, group A consisting of chalcogenides and nitrides of Si, Ge, Sn, Pb,Ga, In, Zn, Cd, Mg, Al, Ba, K, Li, Na, Ca, Sr, Cs, and Rb.
 7. Theorganic electroluminescent device of claim 6, wherein the compounds ofgroup A are selected from the group consisting of chalcogenides andnitrides of Sn, In, and Zn.
 8. The organic electroluminescent device ofclaim 6, wherein either or both of the anode layer and the cathode layerhas a specific resistance of less than 1 Ω·cm.
 9. The organicelectroluminescent device of claim 6, wherein the content of the oxideof Nb is in the range of 0.5 to 30 atomic % for 100 atomic % of thetotal of the anode layer or cathode layer.
 10. The organicelectroluminescent device of c1aim 6, wherein the anode layer or cathodelayer has a thickness in the range of 1 to 100 nm.
 11. The organicelectroluminescent device of claim 6, wherein the anode layer comprisesthe oxide of Nb and the at least one compound selected from the group A.12. An organic electroluminescent device, comprising: a) an anode layer;b) an organic light-emitting layer; c) a cathode layer; and either orboth of a first inorganic thin layer formed between the anode layer andthe organic light-emitting layer, and a second inorganic thin layerformed between the cathode layer and the organic light-emitting layer;the first and second inorganic thin layers comprising at least oneinorganic compound other than In oxides, Sn oxides, Zn oxides, Nioxides, Ti oxides, Zr oxides, Nb oxides, Ta oxides and Sr oxides; anintermediate level of the first inorganic thin layer being smaller thanan ionization potential of the organic light-emitting layer, and greaterthan the work function of the anode; and an intermediate level of thesecond inorganic thin layer being greater than an electron affinity ofthe organic light-emitting layer, and smaller than a work function ofthe cathode.